This invention relates to a device for applying filters to cigarettes, and, more particularly, a device in which the cigarettes and filters are interconnected by adhesive connection bands.
As already known, the application of filters to cigarettes is usually accomplished by so-called filter-applying machines according to the steps briefly described thereinafter.
The cigarettes are placed, two by two, in axial alignment. Between two cigarettes in axial alignment and in contact with the ends thereof a filter section of twice a length as that of a single cigarette is placed. The assembly or unit comprising the two cigarettes and said section is connected by an adhesive band of paper material, wrapped up to cover the filter section and each of said ends for a length of about 1/8". The operations shown are usually carried out while cigarettes and filter sections are retained by suction by the periphery of a longitudinally splined rotating rolling drum.
A fixed concave plate, coaxial with said drum and spaced apart therefrom by a distance substantially equal to the diameter of a cigarette, frictionally engages said units, causing them to roll on the bands, with the latter wrapping up thereabout and connecting the elements thereof.
In the devices of the above described type, said bands are usually provided from a web unwound from a reel, to which a device applies adhesive onto a face prior to cutting.
Due to the very high operating speed attained by modern filter-applying machines, the glue or adhesive on the bands can not sufficiently dry during the short rolling period of said units, where the evaporation of the solvent therein should not be accelerated.
Devices are known in which such a result is achieved by heating said rolling drum, according to the teachings disclosed, for example, in the Italian Pat. No. 697,843, or said fixed plate (German Pat. No. 1,881,457). Both of such devices have disadvantages arising in that, due to the shortness of rolling operation, a sufficient drying of the glue or adhesive can be provided only by extending said rolling beyond the least amount essential for the band wrapping up and/or by using heating means of considerable power.
These expedients may cause damage to the cigarettes since the heating thereof, although limited as far as possible to the filter zone as described in said Italian Pat. No. 697,843, may alter the tobacco quality. In addition, the continued rolling may easily cause tobacco particles to move out of the cigarette ends.
In other known devices, of which one is described for example in U.S. Pat. No. 3,420,243, the heating element comprises a roller operating in combination with a rotary knife to divide the web into bands. A disadvantage of these devices resides in that, due to thermal expansions changing the dimensions of said roller at different operating times of the filter-applying machine, said rotary knife is uncapable of constantly, regularly operating on the web. Then, also any thermal deformation of said roller would adversely affect the cut of the bands.